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The rupture in the water main under Sunset Boulevard is visible where the two pipes converge. The other hole in the pipe, at right, is a result of the Los Angeles Department of Water & Power attempting to plug the flow of water. The broken piece of the pipe is being analyzed to determine the cause of the break, a DWP spokesperson said. Benjamin Brayfield/KPCC

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As UCLA continues to dry out from Tuesday's water main break, Angelenos are once again confronting the realities that a lot of the pipes moving water around town are very old. Orange County and the Inland Empire also have aging pipes.

Every few years, the American Society of Civil Engineers issues report cards on the condition and performance of infrastructure -- from bridges and dams to energy grids and roads. The Inland Empire and Los Angeles County didn’t score higher than a C in recent studies when it came to potable water systems.

"Water pipelines in general have a life expectancy of between 50 and 75 years," says civil engineer Harvey Gobas, who worked on two Infrastructure Report Cards for Los Angeles County, the most recent in 2012. Gobas is now a vice president at Psomas, an L.A.-based Engineering consulting firm.

The water main that burst at UCLA wasn’t just past 90 years old, but faced another Southern California challenge: soil corrosion - the geologic process that creates damage to metals and concrete in direct contact with soil.

"The closer you get to the ocean, usually, the more corrosive the soil," Gobas told KPCC. "UCLA is not that far."

The region's water infrastructure was installed over a long period of time, responding to many different cycles of growth and development in Southern California. It mixes different kinds of pipe - cast iron, ductile iron, composite - that reflect the preferred materials of different eras.

"Obviously, the areas that have developed more recently have newer pipe in the ground, but they're very often still being supplied by pipe that is older," says infrastructure consultant Richard Little, a retired fellow at USC’s Price School of Public Policy.

Little was part of a team that studied a swarm of water main breaks in Los Angeles in 2009. Back then, the state was in another drought, and watering lawns was only allowed two days a week – meaning water pressure would build, causing jolts to the system.

“What we found was when you have pipes that were weakened by age and use and corrosion, when they were subject to an additional stress such as was experienced during the two-day a week watering, they were the first to fail," Little told KPCC.

He says since we’re back in a drought period, he hopes water officials are watching carefully in case the UCLA break is the start of another swarm.